It is known to use valve subassemblies placed in well casing that can be opened once the well casing has been cemented into place. These valve subassemblies or “subs” can use a ball valve seat mechanism that can receive a ball placed into the casing. Once the ball is seated in the valve seat, flow through the valve sub is cut off. The pressure of fracturing fluid injected into the casing will cause the closed valve seat mechanism to slide a piston forward in the valve sub thereby opening ports in the wall of the valve sub to allow the pressure of the fracturing fluid penetrate into a production zone of a hydrocarbon bearing formation. The ball valve seat mechanism can be comprised of varying sized openings. Typically, a number of the valve subs are placed in series in the casing at predetermined intervals in spacing along the well into the formation. The largest diameter valve seat is placed nearest the top of the well with progressively smaller diameter valve seats with each successive valve sub place in the casing string. In this manner, the further valve sub, the one having the smallest diameter opening can be closed by placing the matching sized ball into the casing, which can pass through all of the preceding valve subs, each having larger diameters than the valve sub being closed, until the ball reaches its matching valve sub.
One shortcoming of these known ball valve seat mechanisms is that they cannot be cemented into place with a casing string, as there is no way to clean or wipe the cement out of the valve seat mechanisms. These mechanisms have to be run on a liner with open hole packers in a well bore, which is more costly to carry out.
Another shortcoming is that the volume of fluid, and the rate of fluid flow, is constricted by the progressively decreasing diameter of the ball valve seat mechanism disposed in each of the valve subs, which becomes increasingly restricted with each successive valve sub in the well. While the number of these valve subs can be as high as 23 stages, put in place with a packer system, the flow-rate that can be obtained through these valve subs is not high, for example, a flow rate of 15 cubic meters per minute cannot be obtained through these valve subs.
It is, therefore, desirable to provide a fracturing valve sub that overcomes the shortcomings of the prior art.